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        <p>尝试使用Vue3的新语法-2，使用setup()</p>
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<h2 id="引入setup的原因"><a href="#引入setup的原因" class="headerlink" title="引入setup的原因"></a>引入setup的原因</h2><p>类似<a target="_blank" rel="noopener" href="https://react.docschina.org/docs/hooks-custom.html">React的自定义hooks</a>,有时在不同的组件中需要共用同一逻辑，为了避免不同的逻辑分散在各个组件之中，可以利用setup抽取出公共逻辑。</p>
<p>以React文档中的例子,抽取一个判断用户是否在线的逻辑组件</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> &#123;ref&#125; <span class="keyword">from</span> <span class="string">&#x27;vue&#x27;</span></span><br><span class="line"><span class="keyword">import</span> &#123;getUserStatus&#125; <span class="keyword">from</span> <span class="string">&#x27;@/api/user&#x27;</span></span><br><span class="line"><span class="keyword">export</span> <span class="keyword">default</span> &#123;</span><br><span class="line">  <span class="attr">props</span>:&#123;</span><br><span class="line">    friendID : &#123; <span class="attr">type</span>:<span class="title class_">String</span> &#125; <span class="comment">// prop验证</span></span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="comment">// setup相当于useEffect</span></span><br><span class="line">  <span class="title function_">setup</span>(<span class="params">props</span>)&#123; <span class="comment">// props是父组件传过来的参数</span></span><br><span class="line">    <span class="keyword">const</span> friendID = <span class="title function_">toRef</span>(props,<span class="string">&#x27;friendID&#x27;</span>);</span><br><span class="line">    <span class="keyword">let</span> isOnline = <span class="title function_">ref</span>(<span class="literal">false</span>);<span class="comment">// ref相当于useState，用来在setup中创建响应式变量</span></span><br><span class="line">    <span class="keyword">const</span> fetchIsOnline = <span class="keyword">async</span> () = &gt;&#123;</span><br><span class="line">      isOnline = <span class="keyword">await</span> <span class="title function_">getUserStatus</span>(friendID);</span><br><span class="line">    &#125;;</span><br><span class="line">    <span class="title function_">onMounted</span>(fetchIsOnline);</span><br><span class="line">    <span class="keyword">return</span> &#123;</span><br><span class="line">      isOnline</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="ref-reactive与toRef-toRefs"><a href="#ref-reactive与toRef-toRefs" class="headerlink" title="ref/reactive与toRef/toRefs"></a>ref/reactive与toRef/toRefs</h2><p>ref和reactive分别用来创建组合型或者是单独写法的响应式变量，但是使用reactive时需要注意返回方式和消费者组件的调用方式</p>
<p>单独式写position的写法如下</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 创建</span></span><br><span class="line"><span class="keyword">let</span> x = <span class="title function_">ref</span>(<span class="number">0</span>);</span><br><span class="line"><span class="keyword">let</span> y = <span class="title function_">ref</span>(<span class="number">0</span>);</span><br><span class="line"><span class="comment">// 设置</span></span><br><span class="line">x = <span class="number">1</span>;</span><br><span class="line">y = <span class="number">2</span></span><br><span class="line"><span class="comment">// 返回</span></span><br><span class="line"><span class="keyword">return</span> &#123;</span><br><span class="line">  x,y</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">// 消费</span></span><br><span class="line"><span class="keyword">let</span> &#123;x,y&#125; = <span class="title function_">usePosition</span>();</span><br></pre></td></tr></table></figure>

<p>组合式写法</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 创建</span></span><br><span class="line"><span class="keyword">let</span> position = <span class="title function_">reactive</span>(&#123;</span><br><span class="line">  <span class="attr">x</span>:<span class="number">0</span>,</span><br><span class="line">  <span class="attr">y</span>:<span class="number">0</span></span><br><span class="line">&#125;);</span><br><span class="line"><span class="comment">// 设置</span></span><br><span class="line">position.<span class="property">x</span> = <span class="number">1</span>;</span><br><span class="line">position.<span class="property">y</span> = <span class="number">1</span>;</span><br></pre></td></tr></table></figure>

<p>针对组合式写法必须注意使用的时候如果要解构不能直接解构，而应该使用toRef/toRefs</p>
<p>返回消费方式1</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 返回</span></span><br><span class="line"><span class="keyword">return</span> &#123;</span><br><span class="line">  position</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 消费</span></span><br><span class="line"><span class="keyword">let</span> position = <span class="title function_">usePosition</span>();</span><br><span class="line"><span class="keyword">let</span> &#123;x,y&#125; = <span class="title function_">toRefs</span>(position);</span><br></pre></td></tr></table></figure>

<p>返回消费方式2</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 返回</span></span><br><span class="line"><span class="keyword">return</span> &#123;</span><br><span class="line">  position</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 消费</span></span><br><span class="line"><span class="keyword">let</span> position = <span class="title function_">usePosition</span>();</span><br><span class="line"><span class="keyword">let</span> x = <span class="title function_">toRef</span>(position,<span class="string">&#x27;x&#x27;</span>);<span class="comment">// 参数2就是要解构哪个值出来</span></span><br><span class="line"><span class="keyword">let</span> y = <span class="title function_">toRef</span>(position,<span class="string">&#x27;y&#x27;</span>);</span><br></pre></td></tr></table></figure>

<p>返回消费方式3</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 返回</span></span><br><span class="line"><span class="keyword">return</span> <span class="title function_">toRefs</span>(position)</span><br><span class="line"><span class="comment">// 消费</span></span><br><span class="line"><span class="keyword">let</span> position = <span class="title function_">usePosition</span>();</span><br><span class="line"><span class="keyword">let</span> &#123;x,y&#125; = <span class="title function_">toRefs</span>(position);<span class="comment">// toRefs相当于一次性toRef所有值</span></span><br></pre></td></tr></table></figure>

<p>错误方式</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 返回</span></span><br><span class="line"><span class="keyword">return</span> &#123;</span><br><span class="line">  position</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 消费</span></span><br><span class="line"><span class="keyword">let</span> &#123;x,y&#125; = <span class="title function_">usePosition</span>();<span class="comment">// 不使用toRef而直接解构会失去响应性</span></span><br></pre></td></tr></table></figure>

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